FIG. 9 shows an example of a storage system 10. As shown in the figure, this storage system 10 includes a basic chassis 101 and one or more additional chassis 102 connected by cascading connections with the basic chassis 101. In the basic chassis 101, redundantly configured controllers 11A, 11B, and one or more storage drives 171 are installed. Meanwhile, in the additional chassis 102, redundantly configured enclosures 12A, 12B, and one or more storage drives 171 are installed.
As shown in the above-mentioned figure, each of the controllers (the reference to “A” or “B” for discriminating between the redundantly configured devices are hereinafter omitted unless otherwise required) includes a drive controller 111 and an expander 112. Meanwhile, the enclosure 12 includes an expander 121. The expanders 112 and 121 function as relay devices (data transfer switches) which enable communication (interconnection) between the drive controller 111 and the storage drive 171.
The drive controller 111 receives data input/output requests (data write requests, data read requests, etc.) transmitted from an external device 2 and transmits access requests for the storage drives 171 to the expanders 112 and 121. Furthermore, the drive controller 111 transmits a response to processing for the received data I/O requests (read data, read completion reports, write completion reports, etc.) to the external device 2.
As a storage system including such a configuration, for example, PLT 1 discloses a system including multiple SAS expanders (SAS: Serial Attached SCSI) connected by the cascading connection. The document also refers, as backend processing, to the broadcast frame issued by the SAS expanders when a failure occurs and the discover command issued by the controllers in order to obtain system configuration information.